I think this is really interesting. It's an article in the New York Times about a sonar-mapping project of the Hudson River that has uncovered every ship thought to have sunk there in the last 400 years. The scientists running the project also think they have found a series of walls, clearly of human construction, that date to 3000 years ago.

Check out the whole article, it's great reading. This is what the Internet is for, by golly.